Filter cartridge

ABSTRACT

A filter cartridge comprising a strip, long fiber non-woven fabric which comprises a thermoplastic fiber and in which at least a part of fiber intersections is adhered, which is wound around a perforated cylinder in a twill form, has made it possible to obtain a cylindrical filter cartridge which is excellent in a liquid-passing property, a filter life and a stability in a filtering accuracy. The thermoplastic fiber constituting the above long fiber non-woven fabric is particularly preferably a thermally adhesive composite fiber comprising a low melting point resin and a high melting point resin and having a melting point difference of 10° C. or more between those of both resins.

TECHNICAL FIELD

This invention relates to a filter cartridge for filtering a liquid,more specifically to a filter cartridge prepared by slitting a longfiber non-woven fabric comprising thermoplastic fibers in strips andwinding the slit fabric in a twill form.

BACKGROUND ART

Various filters for clarifying a fluid are presently developed andproduced. Among them, cartridge-type filters (hereinafter called filtercartridges) are widely used in the industrial field, for example, forremoving suspended particles in industrial liquid materials, removingcakes flowing out of a cake filtering apparatus and clarifyingindustrial water.

Several kinds of structures of a filter cartridge have so far beenproposed. The most typical one is a bobbin winder-type filter cartridge,which is a cylindrical filter cartridge prepared by winding a spun yarnas a filter material on a perforated cylindrical core in a twill formand then fluffing the spun yarn. This type has long been used due toinexpensiveness and easiness in production. Another type of structureincludes a non-woven fabric-laminated type filter cartridge. This is acylindrical filter cartridge prepared by winding several kinds ofnon-woven fabrics such as a carding non-woven fabric stepwise andconcentrically on a perforated cylindrical core. A recent advancedtechnique in a non-woven fabric production has allowed some of them tobe put to practical use.

However, the above-mentioned filter cartridges have several defects. Forexample, in the bobbin winder-type filter cartridge for trapping foreignmatters by means of fluffs of fluffed spun yarns and also in gaps of thespun yarns, it is difficult to control the size and form of the fluffsand gaps. This limits size and amount of the foreign matters that can betrapped. Further, constitutional fibers of a spun yarn, which is madefrom short fibers, fall away when fluid flows onto the filter cartridge.Furthermore, in producing a spun yarn, a trace amount of a surfactant isoften applied onto a surface of material short fibers to prevent theshort fibers from sticking to a spinning machine by electrostatic chargeor the like. Filtering a liquid by means of a filter cartridge usingsurfactant-coated spun yarns may bring adverse effects on the cleannessof liquid, such as foaming of the liquid, and increase in TOC (totalorganic carbon), COD (chemical oxygen demand) and the electricconductivity. In addition, a spun yarn is produced by spinning shortfibers as already mentioned, for which at least two steps of forming andspinning short fibers are required. Thus, use of the spun yarn willsometimes increase a price of the product.

In a filter in which a broad non-woven fabric is wound around aperforated cylinder in layers as shown in FIG. 1, a so-called non-wovenfabric-laminated type filter cartridge, its performance depends on thenon-woven fabric used. A non-woven fabric is produced mostly by a methodin which short fibers are confounded by means of a carding machine or anair laid machine and then subjecting them, if necessary, to heattreatment by means of a hot-air heater or a heating roll, or a method inwhich a non-woven fabric is directly prepared, such as a melt blowingmethod and a spun bonding method. However, any machines used forproducing non-woven fabrics, such as a carding machine, an air laidmachine, a hot-air heater, a heating roll, a melt blowing machine and aspun bonding machine, may cause, for example, uneven basis weights of anon-woven fabric in a lateral direction of a machine. Accordingly, afilter cartridge of poor quality will be produced. Also, use of a moreadvanced manufacturing technique to avoid such unevenness sometimesraises the production cost. Moreover, production of one kind ofnon-woven fabric-laminated type filter cartridges needs two to six kindsof non-woven fabrics, and different non-woven fabrics are neededdepending on the kind of a filter cartridge. Thus, the production costwill increase in some cases.

Several methods have been proposed in order to solve such problems ofconventional filter cartridges.

For example, Japanese Patent Publication No. 15004/1988 (U.S. Pat. No.4,278,551) proposes a porous winding cartridge filter comprising atubular member formed from a superimposed winding body of a continuousyarn bundle, whose surface has been modified with cationic colloidalsilica. According to this gazette, the filter has a higher foreignmatter-removing rate than that of conventional bobbin winder filters dueto the cationic silica colloid. However, use of cationic silica colloidis considered to affect cleanness of a liquid as described above.

Further, Japanese Utility Model Publication No. 7767/1994 proposes afilter cartridge in which a filter material obtained by squashing atape-shaped paper having porosity while twisting, thereby squeezing itto control a diameter thereof to about 3 mm is wound around a porousinternal cylinder in a close twill. This method is advantageous in thata winding pitch can be gradually increased from the porous internalcylinder toward the outside. However, the filter material needs to besquashed and squeezed, so that foreign matters are trapped primarilybetween the winding pitches of the filter material. Accordingly, it isless expected to trap foreign matters by the filter material itself asis the case of a conventional bobbin winder type filter using spun yarnswhich traps foreign matters by means of fluffs. This blocks the surfaceof the filter to shorten the filter life or brings about the poorliquid-passing property in a certain case. Japanese Patent PublicationNo. 25607/1989, Japanese Utility Model Publication No. 52090/1991 andJapanese Patent Application Laid-Open No. 317513/1989 concern theinvention analogous to the aforementioned publication, and all thesepublications involve the similar problems.

Alternatively, Japanese Patent Application Laid-Open No. 115423/1989proposes a filter in which strings obtained by slitting a cellulose spunbonded non-woven fabric into strips and passing them through narrowholes to twist them are wound around a bobbin having a lot of drilledpores. It is considered that this method shall make it possible toprepare a filter having a higher mechanical strength and being free ofdissolution in water and elution of a binder, as compared with aconventional roll tissue filter prepared by winding tissue paper in aroll form, which is produced from α-cellulose prepared by refining aconiferous pulp. However, the cellulose spun bonded non-woven fabricused for this filter has a papery form and thus a too high rigidity, sothat it is less expected to trap foreign matters by the filter materialitself as is the case of a conventional bobbin winder type filter usingspun yarns which traps foreign matters by means of fluffs. Further, thecellulose spun bonded non-woven fabric is liable to swell in a liquiddue to its papery form. Swelling may bring about various problems suchas a decrease in a filter strength, a change in a filtering accuracy, adeterioration in a liquid-passing property, a reduction in a filter lifeand the like. Adhesion at fiber intersections of the cellulose spunbonded non-woven fabric are mostly conducted by a certain chemicaltreatment. Such adhesion is often unsatisfactory, causing a change in afiltering accuracy or falling of fiber chips, so that a stable filteringperformance is difficult to achieve. Other inventors propose in JapaneseUtility Model Application Laid-Open No. 36878/1979 a filter using atape-shaped cellulose non-woven fabric without using a binder, but thefilter has the same problem.

Further, Japanese Patent Application Laid-Open No. 45810/1992 proposes afilter prepared by winding a slit non-woven fabric comprising compositefibers in which 10% by weight or more of structural fibers is dividedones of 0.5 denier or less on a porous core cylinder to provide thefiber density of 0.18 to 0.30. This method is advantageously used totrap fine particles contained in a liquid by means of fibers having asmall fineness. However, in order to divide the composite fibers, astress needs to be applied using, for example, high-pressure water, andit is difficult to evenly divide the fibers all over the non-wovenfabric by means of high-pressure water processing. If not evenlydivided, there occurs a difference in a scavenged particle diameterbetween a well-divided portion and an insufficiently divided portion ofthe non-woven fabric, and this may roughen the filtering accuracy.Further, the stress applied for dividing sometimes lowers a strength ofthe non-woven fabric, and this may cause reduction of the resultingfilter strength and frequent deformation of the filter during use; orpossible change of the void ratio of the filter may reduce theliquid-passing property. Further, the reduced strength of the non-wovenfabric makes it difficult to control a tension in winding around aporous core cylinder, and hence the difficulty in exact control of thevoid rate may arise. Further, a spinning technique required forproducing easily divisible fibers and an increased operation cost inproducing thereof lead to an increased production cost of the filter.Such a filter would be usable in a certain field such as thepharmaceutical industry and the electronic industry which require a highfiltering performance, if the above mentioned problems of the filteringperformance are solved. However, such a filter is considered to bedifficult to use in cases in which inexpensive filters are requestedsuch as the filtering of swimming pool water and a plating liquid forthe plating industry. Analogous inventions include Japanese PatentApplication Laid-Open No. 45811/1992, Japanese Utility Model ApplicationLaid-Open No. 131412/1992, Japanese Utility Model Application Laid-OpenNo. 131413/1992, Japanese Utility Model Application Laid-Open No.2715/1993 and Japanese Utility Model Application Laid-Open No.18614/1993, all of which involve the problems described above.

Japanese Patent Application Laid-Open No. 60034/1995 proposes a filterprepared by winding a non-twisted, flat tape-shaped fiber around aporous core cylinder, the tape-shaped fiber being prepared by stericallycrimping an eccentric sheath-core type of combined short fiberscomprising two components with different heat shrinkability. Accordingto this gazette, the filter has less bubbling and less discharged fiberchips than those of conventional filters. However, fibers constitutingthis filter have no adhesion between yarns, though they have a stericcrimping property. Because of this, trapped foreign matters may easilymove into the filtrate when a filtering pressure is raised. JapanesePatent Application Laid-Open No. 328356/1995, analogous to the aboveapplication, also involves the problem described above.

An object of the present invention is to solve the problems describedabove. It has been found, as a result of investigations, that acylindrical filter cartridge which is excellent in a liquid-passingproperty, a filter life and a stability of a filtering accuracy can beobtained by winding a long fiber non-woven fabric comprisingthermoplastic fibers on a perforated cylinder in a twill form. Thisfinding has led to the present invention.

DISCLOSURE OF THE INVENTION

The present invention is composed of:

-   (1) A filter cartridge comprising a strip, long fiber non-woven    fabric which comprises a thermoplastic fiber and in which at least a    part of fiber intersections is adhered, wherein the strip, long    fiber non-woven fabric is wound around a perforated cylinder in a    twill form.-   (2) The filter cartridge as described in item (1), wherein the    thermoplastic fiber constituting the long fiber non-woven fabric is    a thermally adhesive composite fiber comprising a low melting point    resin and a high melting point resin, the difference in a melting    point of both the resins being 10° C. or more.-   (3) The filter cartridge as described in item (2), wherein the low    melting point resin is linear low density polyethylene and the high    melting point resin is polypropylene.-   (4) The filter cartridge as described in any of items (1) to (3),    wherein the long fiber non-woven fabric is bonded by thermal    compression by means of a heat embossing roll.-   (5) The filter cartridge as described in item (2) or (3), wherein    the fiber intersections of the long fiber non-woven fabric are    bonded by hot blast.-   (6) The filter cartridge as described in any of items (1) to (3),    wherein the strip, long fiber non-woven fabric is twisted.-   (7) The filter cartridge as described in any of items (1) to (3),    wherein the strip, long fiber non-woven fabric is formed into a    pleated matter having 4 to 50 pleats and wound around a perforated    cylinder in a twill form.-   (8) The filter cartridge as described in item (7), wherein at least    a part of the pleats of the above pleated matter is non-parallel.-   (9) The filter cartridge as described in item (7), wherein the    pleated matter has a void rate of 60 to 95%.-   (10) The filter cartridge as described in any of items (1) to (3),    wherein the filter cartridge has a void rate of 65 to 85%.-   (11) The filter cartridge as described in any of items (1) to (3),    wherein the long fiber non-woven fabric has a slit width of 0.5 cm    or more, and a product of the slit width (cm) and the basis weight    (g/m²) is 200 or less.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an illustration of a non-woven fabric which is wound in alayer form.

FIG. 2 is an illustration of trapping foreign matters by means of anembossing pattern of a long fiber non-woven fabric.

FIG. 3 is an illustration of winding a strip, long fiber non-wovenfabric as it is, without processing.

FIG. 4 is an illustration of winding a strip, long fiber non-wovenfabric with twisting.

FIG. 5 is an illustration of passing a strip, long fiber non-wovenfabric through a small hole to converge it before winding.

FIG. 6 is an illustration of processing a strip, long fiber non-wovenfabric into a pleated matter by means of a pleat-forming guide.

FIG. 7 is a cross section of a pleat-forming guide used in the presentinvention.

FIG. 8 is a cross section of another pleat-forming guide used in thepresent invention.

FIG. 9 is an illustration of a cross-sectional shape of a pleated matterwith non-parallel pleats.

FIG. 10 is an illustration of a cross-sectional shape of a pleatedmatter with parallel pleats.

FIG. 11 is an illustration of a location of a pleat-forming guide, anarrow rectangular hole and a small hole.

FIG. 12 is a partial cutout perspective of the pleated matter accordingto the present invention.

FIG. 13 is a perspective of the filter cartridge according to thepresent invention.

FIG. 14 is a cross section of the filter cartridge according to thepresent invention.

FIG. 15 is a conceptual diagram of a spun bonded non-woven fabric.

FIG. 16 is a conceptual diagram of a short fiber non-woven fabric.

The codes shall be explained below:

-   1: a part where strong thermal compression bonding by an embossing    pattern is applied.-   2: a part where only weak thermal compression bonding by deviating    from an embossing pattern is applied-   3: foreign matters-   4: foreign matters passing through a part where only weak thermal    compression bonding by deviating from an embossing pattern is    applied-   5: a strip, long fiber non-woven fabric or a converged matter    thereof-   6: a traverse guide of a narrow hole-   7: a bobbin-   8: a perforated cylinder-   9: a filter cartridge-   10: a traverse guide-   11: a traverse guide-   12: external controlling guide-   13: an internal controlling guide-   14: a small hole-   15: a pleated matter-   16: a pleat-forming guide-   17: a comb-shaped pleat-forming guide-   18: a narrow rectangular hole-   19: an oval figure of a minimum area involving a strip, long fiber    non-woven fabric-converged matter-   20: a space between a certain strip, long fiber non-woven    fabric-converged matter and another strip, long fiber non-woven    fabric-converged matter wound on the underneath layer-   21: an internal layer-   22: a fine filtering layer-   23: an external layer-   24: a strip, long fiber non-woven fabric-converged matter-   25: a long fiber constituting a spun bonded non-woven fabric-   26: a particle-   27: a short fiber constituting a short fiber non-woven fabric

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiment of the present invention shall specifically be explainedbelow.

All thermoplastic resins capable of being melt-spun can be used for thethermoplastic resin used in the present invention. Examples includepolyolefin resins such as polypropylene, low density polyethylene, highdensity polyethylene, linear low density polyethylene and copolymerizedpolypropylene (for example, binary or multi-components copolymerscomprising propylene as a primary component with ethylene,butene-1,4-methylpentene-1 and the like); polyester resins such aspolyethylene terephthalate, polybutylene terephthalate and low meltingpoint polyesters thereof copolymerized with addition of isophthalic acidbesides terephthalic acid as an acid component; polyamide resins such asnylon 6 and nylon 66; and thermoplastic resins such as polystyreneresins (atactic polystyrene and syndiotactic polystyrene), polyurethaneelastomers, polyester elastomers and polytetrafluoroethylene. Further,functional resins can also be used so as to provide a filter cartridgewith a biodegradability derived from biodegradable resins such as alactic acid base polyester. Further, polyolefin resins and polystyreneresins which are polymerized using metallocene catalysts are preferablyused for a filter cartridge, taking advantage of the characteristics ofmetallocene resins such as improvements in a strength of a non-wovenfabric and a chemical resistance, and a reduction in a productionenergy. Also, those resins may be blended for use in order to control aheat adhesion property and a rigidity of a long fiber non-woven fabric.When a filter cartridge is used for filtering an aqueous solution ofroom temperature, polyolefin resins such as polypropylene are preferablyused from the viewpoints of a chemical resistance and a cost. When usedfor a solution of a relatively high temperature, polyester resins,polyamide resins or syndiotactic polystyrene resins are preferred.

If the fibers constituting the long fiber non-woven fabric used in thepresent invention are composite fibers comprising a low melting pointresin and a high melting point resin whose melting point difference is10° C. or more, preferably 15° C. or more, heat adhesion in the fiberintersections of the non-woven fabric is strengthened. The melting pointused herein means a peak temperature observed when determining a meltingpoint of a resin by means of a differential scanning type calorimeter(DSC), while in the case of a resin with no distinct peak, it means aflow-starting temperature. The melting point difference has no specificupper limit, which corresponds to a temperature difference between themelting points of the highest melting point and the lowest melting pointamong the thermoplastic resins capable of being melt-spun. In the caseof a resin having no melting point, the flow-starting temperature isdefined as a melting point. Strong heat adhesion in the fiberintersections of non-woven fabrics used for filter cartridges will allowless particles which have been trapped in the vicinity of the fiberintersections to flow out, when a filtering pressure and a flow amountof a solution are elevated, and will result in a less deformation of thefilter cartridge. Further, even if a substance contained in a filtratedeteriorate the fibers, the strong heat adhesion can reduce probabilityof the fibers falling, and thus it is desirable.

A combination of the low melting point resin and the high melting pointresin in the composite fibers shall not specifically be restricted aslong as the melting point difference is 10° C. or more, preferably 15°C. or more, which includes linear low densitypolyethylene/polypropylene, high density polyethylene/polypropylene, lowdensity polyethylene/polypropylene, copolymer of propylene with otherα-olefin/polypropylene, linear low density polyethylene/high densitypolyethylene, low density polyethylene/high density polyethylene,various polyethylenes/thermoplastic polyester,polypropylene/thermoplastic polyester, copolymerizedpolyester/thermoplastic polyester, various polyethylenes/nylon 6,polypropylene/nylon 6, nylon 6/nylon 66 and nylon 6/thermoplasticpolyester. Among them, a combination of linear low-densitypolyethylene/polypropylene is preferably used, since rigidity and a voidrate of the long fiber non-woven fabric can readily be controlled diringa step of fusing fiber intersections in producing the non-woven fabric.When a filter cartridge is applied to a solution of a relatively hightemperature, a combination of low melting point polyester/polyethyleneterephthalate can suitably be used, the polyester being prepared bycopolymerizing ethylene glycol with terephthalic acid and isophthalicacid.

The long fiber non-woven fabric used in the present invention is oneobtained by a spun bonding method and the like. The long fiber non-wovenfabric produced by the spun bonding method and the like has a fiberdirection aligned along a machine direction as shown in FIG. 15, so thata hole constituted by fibers 25 becomes long and narrow, and a maximumsize of the passing particle 26 is rather small. In contrast with this,a non-woven fabric comprising short fibers obtained by a carding methodand the like has a fiber direction not fixed as shown in FIG. 16, sothat a hole constituted by fibers 27 has a shape close to a circle or asquare, and a maximum size of the passing particle 26 is larger thanthat of a long fiber non-woven fabric produced by the spun bondingmethod, even the two has the same aperture rate. A liquid-passingproperty of filter materials is determined substantially by the aperturerate if the fiber diameters are the same, and therefore the long fibernon-woven fabric produced by the spun bonding method can provide afilter having an excellent liquid-passing property. This effect isreduced when an adhesive that clogs holes of a filter is used as abinder, and therefore use of a cellulose spun bonded non-woven fabric isnot desirable. Further, the cellulose spun bonded non-woven fabric isweak in strength, and therefore use of the fabric causes the problemthat the holes constituted by the fibers are liable to be deformed ifthe filtering pressure rises due to clogging of the filter or the like.On the other hand, an average single yarn fineness of the long fibernon-woven fabric used in the present invention may vary depending onapplications of the filter cartridge and the kind of the resins and ispreferably in the range of 0.6 to 3000 dtex. The fineness of 3000 dtexor more provides no difference from a case of a non-woven fabricobtained by merely bundling continuous yarns, thus making it no longeradvantageous to use a long fiber non-woven fabric. The non-woven fabriccan obtain a satisfactory strength by raising the fineness to 0.6 dtexor more, thus allowing easy processing into a pleated matter by a methoddescribed later, and the resulting filter cartridge also has anincreased strength. If a fiber with a fineness less than 0.6 dtex isspun by a current spun bonding method, a processability of a nozzle usedand a spinnability of fibers may be deteriorated, thereby bringing anincrease in cost of a spun bonded non-woven fabric produced.

The structural fibers of the long fiber non-woven fabric do notnecessarily have a circular cross section, and yarns having differentcross sections can also be used. In the latter case, a filter cartridgehaving a higher accuracy than that in case of fibers having a circularcross section, while at the same liquid-passing property, can beproduced, because an amount of trapped fine particles increases as asurface area of the filter becomes larger.

When the long fiber non-woven fabric is made hydrophilic byincorporating a hydrophilic resin such as polyvinyl alcohol into a rawmaterial resin for the fabric or subjecting the surface thereof toplasma treatment, the liquid-passing property can be enhanced in case ofan aqueous solution, and therefore, a filter using such resin ispreferred for filtering an aqueous solution.

A heat bonding method of the fiber intersections in the long fibernon-woven fabric used in the invention includes a thermal compressionbonding method by means of an apparatus such as a thermal embossing rolland a heat flat calender roll and a method using a heat treating machineof a hot blast-circulating type, a heat through-air type, an infraredheater type or a vertical hot blast-blowing type. Among them, a methodusing a thermal embossing roll is preferred, because it can elevate aproduction rate of a non-woven fabric, provides a good productivity andcan reduce a cost.

Further, as shown in FIG. 2, a long fiber non-woven fabric produced bythe method using a thermal embossing roll has part 1 where strongthermal compression bonding by an embossing pattern is applied and part2 where only weak thermal compression bonding by deviating from anembossing pattern is applied. This makes it possible to trap a lot offoreign matters 3, 4 in the part 1, and a part of the foreign matters inthe part 2, while the remaining foreign matters can pass through thelong fiber non-woven fabric to move to the following layer. Preferred isthis deep layer-filtering structure, in which even the inside of thefilter is utilized.

In this case, an embossing patterned area is preferably from 5 to 25%.Setting the lower limit of this area to 5% can enhance the effectexerted by the heat bonding of the fiber intersections, and setting theupper limit to 25% can control the rigidity of the non-woven fabric notto become too high. Further, parts of foreign matters are allowed toeasily pass through the long fiber non-woven fabric, and the foreignmatters passed are trapped in the inside of the filter. This can prolongthe filter life.

The non-woven fabric may be processed into the form of a filtercartridge by a method described later, followed by the thermalcompression bonding of the fiber intersections by means of an infraredray or steam treatment, or the fiber intersections can be chemicallyadhered using an adhesive such as an epoxy resin. The aperture rate inthe latter is lower as compared with a case by thermal bonding, so thatthe liquid-passing property is sometimes lowered.

One of the characteristics of the present invention is to use athermally adhesive composite fiber for the thermoplastic fiberconstituting the non-woven fabric. Use of the thermally adhesivecomposite fiber is advantageous in that the adhesion points remainssmooth because only a part of single yarns is molten by thermal adhesionand that the risk of interfusing the resin into the filtrate due tobreakage of the adhesion points is diminished. A process for producingthis thermally adhesive composite fiber non-woven fabric is disclosed,for example, in Japanese Patent Application Laid-Open No. 88460/1998.

A basis weight of the long fiber non-woven fabric, i.e., a weight perunit area of the non-woven fabric, is preferably 5 to 200 g/m². If thevalue is smaller than 5 g/m², an amount of the fiber is reduced,resulting in an increased unevenness in the non-woven fabric or areduced strength of the non-woven fabric, or occasionally difficulty inthermal bonding of the fiber intersections. On the other hand, the valuelarger than 200 g/m² will render the rigidity of the non-woven fabrictoo much increased, so that the fabric is difficult to wind around aperforated cylinder in a twill form in a later stage.

Next, the long fiber non-woven fabric is formed into strips. Methodsusable for obtaining the strips include one in which a non-woven fabricis directly produced in strips by controlling a spinning width, butpreferably a method in which a broad, long fiber non-woven fabric isslit into strips. In the latter case, the slit width, which variesdepending on the basis weight of the non-woven fabric used, ispreferably 0.5 cm or more. If the width is smaller than 0.5 cm, there isa possibility of cutting the non-woven fabric on slitting. Moreover, itbecomes difficult to control the tension when winding the strip,non-woven fabric in a twill form. Further, when producing filters withthe same void rate, the winding time is longer and the productivity islower. On the other hand, an upper limit of the slit width variesdepending on the basis weight, and a value of the slit width (cm)×basisweight (g/m²) is preferably 200 or less. The value larger than 200 willrender the rigidity of the non-woven fabric excessively increased, sothat winding of the non-woven fabric on a perforated cylinder in a twillform becomes difficult at a later stage. Further, the increased amountof the fiber makes it difficult to wind the non-woven fabric densely.Also, when producing a non-woven fabric in the form of strips bycontrolling the spinning width, the preferred ranges of the basis weightand the non-woven fabric width are the same as those in the case ofpreparing the strips by slitting.

This long fiber non-woven fabric may be wound in a twill form afterprocessing by a method, which shall be described later, or it may bewound as it is without processing. One embodiment of the productionprocess is shown in FIG. 3. A winder conventionally used for a bobbinwinder type filter cartridge can be used for the winding machine. Astrip, long fiber non-woven fabric 5 fed passes through a narrow-holedtraverse guide 6, which moves with twilling while traversing, and thenis wound around a perforated cylinder 8 mounted on a bobbin 7 to form afilter cartridge 9. The filter cartridge produced by this process isvery dense and has a fine accuracy. However, it is difficult in thisprocess to change the winding number to control the filtering accuracy.

On the other hand, this strip, long fiber non-woven fabric can betwisted and then wound. One embodiment of the production process isshown in FIG. 4. Also in this case, a winder conventionally used for abobbin winder type filter cartridge can be used for the winding machine.The non-woven fabric becomes apparently thick by twisting, and thereforea traverse guide 10 has preferably a larger hole diameter than that inthe case of FIG. 3. By twisting a non-woven fabric, an apparent voidrate of the non-woven fabric can be changed depending on a twistingnumber per unit length or a twisting strength, so that the filteringaccuracy can be controlled. The twisting number in this case fallspreferably in a range of 50 to 1000 times per meter of the strip, longfiber non-woven fabric. If this value is smaller than 50 times, thetwisting effect is scarcely obtained. On the other hand, the valuelarger than 1000 times will provide the filter cartridge produced with arough liquid-passing property. Accordingly, both are not preferred.

It is more preferred to converge the strip, long fiber non-woven fabricdescribed above by any method and then wind it around a perforatedcylinder. Such a method include one in which the strip, non-woven fabricmay be passed merely through a small hole to be converged or one inwhich the cross-sectional form of the strip, long fiber non-woven fabricmay be pre-molded by means of a pleat-forming guide and then passedthrough a small hole to be processed into a pleated matter. Use of thelatter method makes it possible to control a ratio of a traversing speedof the traverse guide to a rotating speed of the bobbin to change thewinding pattern, so that filter cartridges having various performancescan be produced from the same kind of the strip, long fiber non-wovenfabric.

One embodiment of a production process in which the non-woven fabric ispassed merely through a small hole for converging the strip is shown inFIG. 5. Also in this case, a winder conventionally used for a bobbinwinder type filter cartridge can be used for the winding machine. InFIG. 5, the hole of a traverse guide 11 turned into a small hole,thereby converging the strip, long fiber non-woven fabric, but a guideof a small hole may be provided at a yarn passage in front of thetraverse guide 11. The diameter of the small hole varies depending onthe basis weight and the width of the non-woven fabric used and fallspreferably in the range of 3 to 10 mm. If this diameter is smaller than3 mm, a friction between the non-woven fabric and the small hole isincreased, so that the winding tension becomes too high. On the otherhand, the value larger than 10 mm may not render the converging size ofthe non-woven fabric stabilized.

Shown in FIG. 6 is one embodiment of a production process in which thecross-sectional form of the strip, long fiber non-woven fabric ispre-molded by means of a pleat-forming guide and then processed into apleated matter. Also in this case, a winder conventionally used for abobbin winder type filter cartridge can be used for the winding machine.In this process, the cross-sectional form of the strip, long fibernon-woven fabric 5 is pre-molded through a pleat-forming guide 16 andthen passed through a small hole 14 to be formed into a pleated matter15. The pleated matter 15 is drawn toward a direction A to pass througha traverse guide and to wind around a perforated cylinder to prepare afilter cartridge. In FIG. 6, a heavy line represents a fold of thenon-woven fabric, and a gray part represents the non-woven fabric.

Next, the pleat-forming guide described above shall be explained.Usually, the pleat-forming guide is prepared by subjecting the surfaceof a processed round bar having a major diameter of about 3 to 10 mm tothe 1 fluorocarbon resin treatment in order to prevent friction with anon-woven fabric. Examples of its form are shown in FIGS. 7 and 8. Inthese examples, the pleat-forming guide 16 comprises an externalcontrolling guide 12 and an internal controlling guide 13. The form ofthe pleated forming guide 16 shall not specifically be restricted and ispreferably one in which the non-woven fabric is converged in such amanner that the cross-sectional form of the pleated matter producedthrough this guide shows no parallel pleats. Examples of thecross-sectional form of the pleated matter thus produced are shown inFIGS. 9 (A), (B) and (C), but shall not be restricted to these. In themost preferred embodiment of the present invention, the non-woven fabricis converged to form the pleated matter in which at least a part of thepleats is non-parallel. That is, when the pleats is partiallynon-parallel as shown in the cross-sectional forms in FIG. 9, thepleated matter can keep a stronger form-holding power even when afiltering pressure is applied from a vertical direction as shown by anarrow, as compared with the cases in FIGS. 10 (A) and (B), in whichalmost all of the pleats are parallel, so that the filtering performancein the original pleated form can be maintained. In the case where thepleats are non-parallel, the ability to control the pressure loss of thefilter cartridge is better than that of the base where the pleats areparallel, and therefore it is particularly preferred that the pleatedmatter has the cross-sectional form showing non-parallels pleats. Thenumber of the guide is not limited to one, and it is preferable thatseveral guides with different forms and sizes are arranged in series togradually change the cross-sectional form of the strip, long fibernon-woven fabric, so that the cross-sectional form of the pleated mattercan be kept uniform, and unevenness in the quality can be removed.

In the present invention, when the strip, long fiber non-woven fabric isformed into the pleated matter and then wound around the perforatedcylinder, the final pleat number of the pleated matter is 4 to 50,preferably 7 to 45. If the pleat number is less than 4, the effect ofexpanding a filtering area by pleating is poor. On the other hand, ifthe pleat number exceeds 50, too small pleats make the production of thefilter cartridge difficult, and tend to adversely affect the filteringperformance to lower.

A comb-shaped pleat-forming guide 17 as shown in FIG. 11, for example,can be used to provide the long fiber non-woven fabric with many pleats,and then the non-woven fabric is passed through a narrower rectangularhole 18 to be deformed so as to provide more pleats, which arenon-parallel at random.

The pleated matter 15 which has passed through the small hole 14described above can be heat-processed by means of hot blast or aninfrared heater to fix the cross-sectional form of the pleated matter.This step is not requisite, but it is desirable in case of making acomplicated cross-sectional form of the pleated matter or in case ofusing the strip, long fiber non-woven fabric having a high rigidity,because the cross-sectional form is liable to be broken and deviatedfrom the designed form.

The void rate of the strip, long fiber non-woven fabric which has beenconverged or the pleated matter, used in the present invention,(hereinafter referred to as a strip, long fiber non-wovenfabric-converged matter) shall be explained. First, the cross-sectionalarea of the strip, long fiber non-woven fabric-converged matter isdefined, as shown in FIG. 12, by the area of the smallest oval FIG. 19(the oval figure means a polygon in which all the respective internalangles fall within 180 degrees) containing a strip, long fiber non-wovenfabric-converged matter 24. The strip, long fiber non-wovenfabric-converged matter is cut to a prescribed length, for example, alength as large as 100 times of the square root of the cross-sectionalarea and the void rate is defined according to the following equation:(Apparent volume of strip, long fiber non-woven fabric-convergedmatter)=(Cross-sectional area of strip, long fiber non-wovenfabric-converged matter)×(Cut length of strip, long fiber non-wovenfabric-converged matter);(Real volume of strip, long fiber non-woven fabric-convergedmatter)=(Weight of cut strip, long fiber non-woven fabric-convergedmatter)/(Density of raw material for strip, long fiber non-wovenfabric-converged matter);(Void rate of strip, long fiber non-woven fabric-convergedmatter)={1−(Real volume of strip, long fiber non-woven fabric-convergedmatter)/(Apparent volume of strip, long fiber non-woven fabric-convergedmatter)}×100 (%).

The void rate defined according to the equation is preferably 60 to 95%,more preferably 85 to 92%. Setting the lower limit of the value to 60%makes it possible to inhibit the strip, long fiber non-wovenfabric-converged matter from becoming excessively dense, to sufficientlycontrol the possible pressure loss when used for a filter cartridge andto more elevate the foreign matter-trapping efficiency of the strip,long fiber non-woven fabric-converged matter. Further, setting the upperlimit to 95% makes it easy to wind the converged matter at a later stageand makes it possible to lessen the possible deformation of the filterby loaded pressure when used for a filter cartridge. An example of amethod for controlling this includes controlling of the winding tensionand adjusting the guide form of the pleat-forming guide.

Further, when producing the above strip, long fiber non-wovenfabric-converged matter, granular activated carbon or ion exchangeresins may be present as long as they do not damage the effects of thepresent invention. In this case, in order to fix granular activatedcarbon or ion exchange resins, they may be adhered by means of asuitable binder either prior to or after converging the strip, longfiber non-woven fabric or processing it into a pleated matter, or theymay be first added and then thermally adhered to the structural fibersof the long fiber non-woven fabric by heating.

The strip, long fiber non-woven fabric-converged matter should notnecessarily be produced by a continuous process, if any contrivance toretain the cross-sectional form is made, and it may be first woundaround a suitable bobbin and then rewound by means of a winder.

The method of winding the strip, long fiber non-woven fabric shall beexplained. A perforated cylinder having a diameter of about 10 to 40 mmand a length of 100 to 1000 mm is installed to a bobbin of this winder,and the strip, long fiber non-woven fabric (or the strip, long fibernon-woven fabric-converged matter) passed through a yarn passage of thewinder is fixed at an end part of the perforated cylinder. Theperforated cylinder functions as a core of a filter cartridge, and thematerial and the form thereof shall not specifically be restricted aslong as it has a strength which is endurable to external pressureapplied in filtering and the pressure loss is not markedly high. It maybe, for example, an injection-molded article obtained by processingpolyethylene or polypropylene into a net type cylinder as is the casewith a core used for a conventional filter cartridge or ones obtained byprocessing ceramics and stainless steel in the same manner.Alternatively, other filter cartridges such as a filter cartridgesubjected to pleat-folding processing and a filter cartridge of anon-woven fabric-winding type can be used as a perforated cylinder. Theyarn passage of the winder is waved in twill form by means of a traversecum disposed parallel to the bobbin, so that the strip, long fibernon-woven fabric is wound around the perforated cylinder while waving ina twill form. The winding conditions in this case can be set upaccording to those in producing a conventional bobbin winder type filtercartridge. Initial speed of the bobbin may be set to, for example, 1000to 2000 rpm, and the feeding speed may be controlled to apply a tensionin winding the non-woven fabric. The void rate of the filter cartridgecan be changed by the tension in this case. Further, the tension inwinding is controlled to make the void rate of an internal layer small,and the void rate of an intermediate layer to an external layergradually large as the non-woven fabric is wound around. In particular,when the strip, long fiber non-woven fabric is first formed into thepleated matter and then is wound around the perforated cylinder, therecan be provided a filter cartridge having an ideal filtering structureowing to a difference in rough and dense structures formed in theexternal layer, the intermediate layer and the internal layer incombination with a deep layer-filtering structure formed by the pleatsof the pleated matter. The filtering accuracy can be changed bycontrolling a ratio of the traversing speed of the traverse cum to therotating speed of the bobbin, thereby changing the winding pattern. As apatterning method, a known method used in a conventional bobbin windertype filter cartridge can be used. If the filter has a fixed length, thepattern can be shown in terms of the winding number. When a space 20(FIG. 13) between a certain yarn (the strip, long fiber non-woven fabricin case of the present invention) and a yarn wound on an underneathlayer is broad, the filtering accuracy is roughened. On the contrary,when the space is narrow, the filtering accuracy becomes fine. Usingthese methods, the strip, long fiber non-woven fabric is wound aroundthe perforated cylinder 8 (FIG. 13) to form a filter cartridge having amajor diameter 1.5 to 3 times as large as that of the perforatedcylinder. This may be used for the filter cartridge 9 (FIG. 13) as itis, or a gasket of foamed polyethylene having a thickness of 3 mm may bestuck on an end surface of the filter cartridge to improve an adhesiveproperty to housing.

The filter thus prepared has a void rate preferably in the range of 65to 85%. The value smaller than 65% will render the fiber density toohigh, so that the liquid-passing property is reduced. On the contrary,the value larger than 85% will render the strength of the filtercartridge to reduce and often cause deformation of the filter cartridgewhen a high filtering pressure is applied.

The liquid-passing property can be improved by providing the strip, longfiber non-woven fabric with cut or by perforating it. In this case, thenumber of the cut is preferably 5 to 100 per 10 cm of the non-wovenfabric, and the perforation area is preferably 10 to 80%. The filteringperformance can be controlled by winding plural sheets of the strip,long fiber non-woven fabric or winding it together with other yarns suchas a spun yarn. Further, as shown in FIG. 14, a filter cartridge can beformed by winding the non-woven fabric in the following manner; thenon-woven fabric 5 is wound around the perforated cylinder 8 in atraversing manner to form the internal layer 21 with a suitablediameter; subsequently, a wide non-woven fabric is wound around theinternal layer in a layer form to form the fine filtering layer 22; thenthe non-woven fabric 5 is wound again around the filtering layer in atraversing manner to form the external layer 23. When a filter cartridgehaving a rough accuracy is prepared using the wide non-woven fabricwhich is wound in a non-layer form with a broad space between yarns, amaximum flowing-out diameter of particles sometimes becomes extremelylarge, while by using the wide non-woven fabric wound in a layer form,the maximum flow-out diameter of particles can finely be controlled asrequired.

The present invention shall be explained below in detail with referenceto examples and comparative examples, but the present invention shallnot be restricted to these examples. In the respective examples, thephysical properties and the filtering performances of the filters wereevaluated by the methods described below. Basis weight and thickness ofnon-woven fabric:

The non-woven fabric having the area of 625 cm² was cut off and weighed.The weight was converted to a weight per square meter to define a basisweight. Further, the thickness of the cut non-woven fabric was measuredat 10 optional points, and the values at 8 points excluding the maximumvalue and the minimum value were averaged to define the thickness (μm)of the non-woven fabric.

Fineness of Non-Woven Fabric:

The non-woven fabric was sampled at 5 spots at random, and they werephotographed through a scanning type electron microscope. 20 fibers perspot were selected at random to measure the diameters of the fibers, andan average value thereof was defined as the fiber diameter (μm) of thenon-woven fabric. The fineness (dtex) was determined from the followingequation using the fiber diameter thus obtained and the density (g/cubiccentimeter) of the raw material resin of the non-woven fabric:(Fineness)=π(Fiber diameter)²×(Density)/400Number of Pleats in Pleated Matter:

The cross-sectional form of the pleated matter was fixed by an adhesiveand then cut at 5 optional spots to photograph the cross sectionsthereof. The fold number of the strip, long finer non-woven fabric wascounted from the photographs, counting either of inverted V folding andV folding as one, and a half of the average number in the five cut spotsis defined as the number of pleats.

Cross-Sectional Area and Void Rate of Strip, Long Fiber Non-WovenFabric-Converged Matter:

The cross-sectional form of the strip, long fiber non-wovenfabric-converged matter was fixed by an adhesive and then cut at 5optional spots to photograph the cross sections thereof. The photographswere subjected to image analysis to determine the cross-sectional areaof the strip, long fiber non-woven fabric-converged matter. Further,another 10 cm length of the strip, long fiber non-woven fabric-convergedmatter was cut at a different spot to determine the void rate from itsweight and the above cross-sectional area using the following equation:(Apparent volume of strip, long fiber non-woven fabric-convergedmatter)=(Cross-sectional area of strip, long fiber non-wovenfabric-converged matter)×(Cut length of strip, long fiber non-wovenfabric-converged matter);(Real volume of strip, long fiber non-woven fabric-convergedmatter)=(Weight of strip, long fiber non-woven fabric-convergedmatter)/(Density of raw material for strip, long fiber non-wovenfabric-converged matter);(Void rate of strip, long fiber non-woven fabric-convergedmatter)={1−(Real volume of strip, long fiber non-woven fabric-convergedmatter)/(Apparent volume of strip, long fiber non-woven fabric-convergedmatter)}×100 (%).Yarn Space:

A space (shown by numeral 20 in FIG. 13) between the strip, long fibernon-woven fabric-converged matter (or the matters wound around theperforated cylinder such as the strip, long fiber non-woven fabric andthe spun yarn in the following examples) situated on the surface and thestrip, long fiber non-woven fabric-converged matter adjacent thereto wasmeasured at 10 spots per one filter cartridge, and the average thereofwas calculated to obtain the yarn space.

Void Rate of Filter Cartridge:

The major diameter, the minor diameter, the length and the weight weremeasured to determine the void rate using the following equation. Inorder to determine the void rate of the filter itself, the majordiameter of the perforated cylinder was used for the value of the minordiameter, and a value obtained by deducting the weight of the perforatedcylinder from the weight of the filter cartridge was used for the valueof the weight:(Apparent volume of filter)=π{(Major diameter of filter)²−(Minordiameter of filter)²}×(Filter length)/4;(Real volume of filter)=(Filter weight)/(Density of raw material offilter);(Void rate of filter)={1−(Real volume of filter)/(Apparent volume offilter)}×100 (%).Initial Trapped Particle Diameter, Initial Pressure Loss and FilterLife:

One filter cartridge was mounted to a housing of a circulating typetesting machine for filtering performance, and water was passed tocirculate, controlling a flow rate to 30 liter/minute by means of apump. A pressure loss between the pressures at the inlet and outlet ofthe filter cartridge was set as an initial pressure loss. Next, a cakeprepared by mixing 8 kinds of testing powder I prescribed in JIS Z 8901(abbreviated as JIS 8 kinds; intermediate diameter: 6.6. to 8.6 μm) with7 kinds of the same powder (abbreviated as JIS 7 kinds; intermediatediameter: 27 to 31 μm) in a weight ratio of 1:1 was continuously addedat 0.4 g/minute, and the original solution and the filtrate were sampled5 minutes after starting of the addition. They were diluted toprescribed concentrations, and then the numbers of particles containedin the respective solutions were measured by means of a light shieldingtype particle detector to calculate an initial trapping efficiency ineach particle diameter. Further, the value thereof was interpolated todetermine a particle diameter showing a trapping efficiency of 80%. Theaddition of the cake was still continued until the pressure loss of thefilter cartridge reached to 0.2 MPa, and the original solution and thefiltrate were again sampled to determine a trapped particle diameter.Time consumed from starting addition of the cake until reaching to 0.2MPa was defined as a filter life. When the pressure difference did notreach to 0.2 MPa even the filter life reached to 1000 minutes, themeasurement was discontinued at that point of time. Bubbling of initialfiltrate and fiber falling:

One filter cartridge was mounted to a housing of a circulating typetesting machine for filtering performance, and ion-exchanged water waspassed, controlling a flow rate to 10 liter/minute by means of a pump.One liter of an initial filtrate was sampled, and 25 cm³ thereof wastaken into a colorimetric bottle and stirred vigorously to observebubbling at 10 seconds after stopping the stirring. When a volume ofbubble (volume from a liquid surface up to the top of bubble) was 10 cm³or more, it was judged poor and shown by a symbol “×”; when a volume ofbubble was less than 10 cm³, it was judged fair and shown by a symbol“Δ”; and when less than 5 bubbles having a diameter of 1 mm or more wereobserved, it was judged good and shown by a symbol “◯”. Further, 500 cm³of the initial filtrate was passed through a nitrocellulose filterhaving a pore diameter of 0.8 μm to judge fiber falling, wherein thenumber of fibers having a length of 1 mm or more per cm² of the filterpaper were 4 or more was judged poor and shown by “×”; the number of 1to 3 was judged fair and was shown by “Δ”; and the number of 0 wasjudged good and shown by “◯”.

EXAMPLE 1

Used as a long fiber non-woven fabric was a polypropylene spun bondednon-woven fabric having a basis weight of 22 g/m², a thickness of 200 μmand a fineness of 2 dtex, in which fiber intersections were bonded byheat compression by means of a heat embossing roll. Used for aperforated cylinder was a polypropylene injection-molded article havinga minor diameter of 30 mm, a major diameter of 34 mm and a length of 250mm, and also having 180 holes of 6 mm square. The above non-woven fabricwas slit to a width of 50 mm to obtain a strip, long fiber non-wovenfabric. A winder was used to wind the strip, long fiber non-woven fabricaround the perforated cylinder without converging. It was wound aroundthe perforated cylinder at an initial spindle velocity of 1500 rpm untilthe major diameter reached to 62 mm, while controlling the windingnumber to 3 and 3/11 so that a space between the non-woven fabrics was 0mm, and there was provided a cylindrical filter cartridge 9 as shown inFIG. 13.

EXAMPLE 2

A filter cartridge was obtained in the same manner as in Example 1,except that the winding number was changed to 4 and 3/7. However, thefiltering performance was not much different from that of the filterdescribed in Example 1. The reason is considered to be that the stripnon-woven fabric was not converged and this does not influence on thewinding number.

EXAMPLE 3

The same strip, long fiber non-woven fabric and the same perforatedcylinder as used in Example 1 were used. A guide of a circular holehaving a diameter of 5 mm was disposed on a yarn passage communicatingto the winder to converge the non-woven fabric to a diameter of 5 mm,and it was wound around the perforated cylinder under the sameconditions as in Example 1 to obtain a cylindrical filter cartridge.This filter had almost the same filtering performance as that of thefilter obtained in Example 1.

EXAMPLE 4

A cylindrical filter cartridge was obtained in the same manner as inExample 3, except that the winding number was changed to 4 and 3/7 so asto set the space between the strip, long fiber non-woven fabrics to 1mm. This filter had a rougher accuracy, a better liquid-passing propertyand a longer filter life than those of the filter described in Example3.

EXAMPLE 5

A cylindrical filter cartridge was obtained in the same manner as inExample 3, except that the winding number was changed to 4 and 2/7 so asto set the space between the strip, long fiber non-woven fabrics to 2mm. This filter was much rougher than the filter described in Example 4.

EXAMPLE 6

A cylindrical filter cartridge was obtained in the same manner as inExample 3, except that the winding number was changed to 3 and 5/7 so asto set the space between the strip, long fiber non-woven fabrics to 2mm. This filter was much rougher than the filter described in Example 5.

EXAMPLE 7

A cylindrical filter cartridge was obtained in the same manner as inExample 4, except for changing the raw material resin of the long fibernon-woven fabric to nylon 66. This filter showed almost the samefiltering performance as that of the filter described in Example 4.

EXAMPLE 8

A cylindrical filter cartridge was obtained in the same manner as inExample 4, except that the raw material resin of the long fibernon-woven fabric was changed to polyethylene terephthalate. This filtershowed almost the same filtering performance as that of the filterdescribed in Example 4.

EXAMPLE 9

A cylindrical filter cartridge was obtained in the same manner as inExample 4, except that the long fiber non-woven fabric was slit to awidth of 10 mm and that the winding number was changed to 3 and 10/21 soas to set the yarn space to 1 mm. This filter had almost the sameperformance as that of the filter described in Example 4. However, timerequired for winding was longer than in Example 4.

EXAMPLE 10

A cylindrical filter cartridge was obtained in the same manner as inExample 3, except that the long fiber non-woven fabric was slit to awidth of 100 mm and that the winding number was changed to 3 and 5/7 soas to set the yarn space to 0 mm. This filter had a rougher accuracythan that of the filter described in Example 3 and showed an accuracyclose to that of the filter described in Example 5.

The filter having a rough accuracy was obtained, in spite of setting theyarn space to 0 mm. This is because the strip, long fiber non-wovenfabric-converged matter became extremely thick.

EXAMPLE 11

A cylindrical filter cartridge was obtained in the same manner as inExample 4, except that sheath-core type composite fibers comprisinghigh-density polyethylene as a low melting point component andpolypropylene as a high melting point component in a weight ratio of 5:5were used as the structural fibers for the long fiber non-woven fabric.This filter had a more excellent accuracy than that of the filterdescribed in Example 4 and showed such an excellent stability in thefiltering accuracy that the trapped particle diameter at 0.2 MPascarcely changed from the initial trapped particle diameter.

EXAMPLE 12

A cylindrical filter cartridge was obtained in the same manner as inExample 11, except that linear low-density polyethylene (melting point:125° C.) was used as the low melting point component. This filter hadalmost the same filtering accuracy as that of the filter obtained inExample 11 and showed a more excellent liquid-passing property than thatof the filter described in Example 11.

EXAMPLE 13

A cylindrical filter cartridge was obtained in the same manner as inExample 12, except that a heat compression bonding method for the fiberintersections was changed from the heat embossing roll to a hotblast-circulating type heating apparatus. This filter had a littlerougher accuracy than that of the filter described in Example 12.

EXAMPLE 14

A cylindrical filter cartridge was obtained in the same manner as inExample 4, except that the fineness of the long fiber non-woven fabricwas changed to 10 dtex. This filter had a rougher accuracy than that ofthe filter described in Example 4.

EXAMPLE 15

A cylindrical filter cartridge was obtained in the same manner as inExample 4, except that the basis weight of the long fiber non-wovenfabric was changed to 44 g/m². This filter had a rougher accuracy thanthat of the filter described in Example 4, but showed almost the sameaccuracy as that of the filter described in Example 10.

EXAMPLE 16

A cylindrical filter cartridge was obtained in the same manner as inExample 4, except that the strip, long fiber non-woven fabric wastwisted 100 times per one meter, instead of converging the non-wovenfabric. This filter showed almost the same performance as that of thefilter described in Example 4.

EXAMPLE 17

A cylindrical filter cartridge was obtained in the same manner as inExample 4, except that the strip, long fiber non-woven fabric wasprocessed to a cross-sectional form as shown in FIG. 10 (A) to obtain apleated matter having a pleat number of 4 and that the above pleatedmatter was used for the converged strip, long fiber non-woven fabric.This filter had a little more excellent accuracy than that of the filterdescribed in Example 4, but showed a shorter filter life. The filterlife was shorter than that of the filter described in Example 4. This isbecause the pleated matter had parallel pleats and thus a filteringpressure was applied in a direction vertical to the pleats so that thevoid rate of the filter is reduced.

EXAMPLE 18

A cylindrical filter cartridge was obtained in the same manner as inExample 17, except that the strip, long fiber non-woven fabric wasprocessed to a cross-sectional form as shown in FIG. 9 (A) to obtain apleated matter having a pleat number of 7 to be used in the presentexample. This filter had a little finer accuracy than that of the filterdescribed in Example 4, but was an excellent filter having the sameliquid-passing property and filter life as those of the filter describedin Example 4.

EXAMPLE 19

A cylindrical filter cartridge was obtained in the same manner as inExample 17, except that the strip, long fiber non-woven fabric wasprocessed to a cross-sectional form as shown in FIG. 9 (C) to obtain apleated matter having a pleat number of 15 to be used in this example.This filter had a much finer accuracy than that of the filter describedin Example 18 but was an excellent filter having the same liquid-passingproperty and filter life as those of the filter described in Example 4.

EXAMPLE 20

A cylindrical filter cartridge was obtained in the same manner as inExample 19, except that the pleat number of the strip, long fibernon-woven fabric was changed to 41. This filter had a finer accuracythan that of the filter described in Example 19, but was an excellentfilter having the same liquid-passing property and filter life as thoseof the filter described in Example 4.

EXAMPLE 21

A cylindrical filter cartridge was obtained in the same manner as inExample 19, except that the strip, long fiber non-woven fabric wasdensely converged to control the void rate of the pleated matter to 72%.This filter is rougher than the filter described in Example 19.

COMPARATIVE EXAMPLE 1

A cylindrical filter cartridge was obtained in the same manner as inExample 4, except that polypropylene spun yarns having a diameter of 2mm obtained by spinning fibers having a fineness of 3 dtex was used inplace of the strip, long fiber non-woven fabric and that the yarn spacewas set to 1 mm. This filter had an initial trapped particle diameterrougher than that of the filter described in Example 4 and almost thesame as that of the filter described in Example 5. However, it had aninferior liquid-passing property and a shorter filter life than those ofthe filter described in Example 5. Further, bubbling was observed in theinitial filtrate, and falling of the filter material was observed aswell.

COMPARATIVE EXAMPLE 2

A cylindrical filter cartridge was obtained in the same manner as inExample 4, except that a filter paper No. 1 prescribed in JIS P 3801,which was cut to a width of 50 mm, was used in place of the strip, longfiber non-woven fabric. This filter had an initial trapped particlediameter finer than that of the filter described in Example 4 androugher than that of the filter described in Example 3. However, theinitial pressure loss was large, and the trapped particle diameter at anelevated pressure was changed from the initial one to a large extent.Further, the filter life was extremely short, and falling of the filtermaterial was observed in the initial filtrate.

COMPARATIVE EXAMPLE 3

short fibers comprising polypropylene and high-density polyethylenewhich were dividable to eight parts and had a fineness of 4 dtex werewebbed by means of a carding machine, and the webbed matter wassubjected to fiber division and fiber entanglement by high pressurewater processing to obtain a divided short fiber non-woven fabric havinga basis weight of 22 g/m². This non-woven fabric was observed under anelectron microscope to carry out image analysis, which showed that 50%by weight of the whole fibers was divided into a fineness of 0.5 dtex. Acylindrical filter cartridge was obtained in the same manner as inExample 4, except that this non-woven fabric was cut to a width of 50 mmand used in place of the strip, long fiber non-woven fabric. An initialtrapped particle diameter in this filter was smaller than that in thefilter described in Example 4, but a trapped particle diameter at 0.2MPa was larger. Further, a little bubbling in the initial filtrate wasobserved as well as falling of the fibers.

COMPARATIVE EXAMPLE 4

The long fiber non-woven fabric used in Example 1 was slit to a width of25 cm, and the cut long fiber non-woven fabric was wound around theperforated cylinder in a layer form at a line pressure of 1.5 kg/m asshown in FIG. 1 to obtain a cylindrical filter cartridge. An initialtrapped particle diameter in this filter was almost the same as that inthe filter described in Example 4, but a trapped particle diameter at0.2 MPa was larger. The filter life was a little shorter as comparedwith that in Example 4.

The results obtained in the examples and the comparative examples areshown in Tables 1 and 2.

TABLE 1 Long fiber non-woven fabric Processing of non-woven fabric BasisSlit Void weight Thickness Fineness Adhesion at width Cross- Pleat rate(g/m²) (μm) (dtex) intersection Resin (mm) sectional form number (%)Example 1 22 200 2 Emboss PP 50 None — — Example 2 22 200 2 Emboss PP 50None — — Example 3 22 200 2 Emboss PP 50 Converged — 91 Example 4 22 2002 Emboss PP 50 Converged — 90 Example 5 22 200 2 Emboss PP 50 Converged— 90 Example 6 22 200 2 Emboss PP 50 Converged — 91 Example 7 22 200 2Emboss Nylon 66 50 Converged — 90 Example 8 22 200 2 Emboss PET 50Converged — 89 Example 9 22 200 2 Emboss PP 10 Converged — 90 Example 1022 200 2 Emboss PP 100 Converged — 91 Example 11 22 200 2 Emboss HDPE/PP50 Converged — 90 Example 12 22 200 2 Emboss LLDPE/PP 50 Converged — 90Example 13 22 200 2 TA LLDPE/PP 50 Converged — 90 Example 14 22 200 10Emboss PP 50 Converged — 90 Example 15 44 400 2 Emboss PP 25 Converged —90 Example 16 22 200 2 Emboss PP 50 Twisted — — Example 17 22 200 2Emboss PP 50  FIG. 10-(A) 4 90 Example 18 22 200 2 Emboss PP 50 FIG.9-(A) 7 95 Example 19 22 200 2 Emboss PP 50 FIG. 9-(C) 15 90 Example 2022 200 2 Emboss PP 50 FIG. 9-(C) 41 91 Example 21 22 200 2 Emboss PP 50FIG. 9-(C) 15 72 Comparative (PP spun yarn used) PP (PP spun yarn used)Example 1 Comparative 90 200 — (Filter Cellulose  15 None — — Example 2paper No. 1) Comparative 22 200 0.5 WJ HDPE/PP  50 None — — Example 3Comparative 22 200 2 Emboss PP (250) None — — Example 4

TABLE 2 Filtering performance Winding Initial Initial Trapped YarnFilter trapped pressure particle Filter space void rate particle lossdiameter in life Fiber (mm) (%) diameter (μm) (MPa) 0.2 MPa (μm)(minute) Bubbling falling Example 1 0 78 7.1 0.013 8 75 ∘ ∘ Example 2 178 7.1 0.013 8 75 ∘ ∘ Example 3 0 78 8.2 0.011 9 75 ∘ ∘ Example 4 1 8213 0.003 14 225 ∘ ∘ Example 5 2 83 17 0.001 19 650 ∘ ∘ Example 6 3 83 300.001 30 >1000 ∘ ∘ Example 7 1 82 13 0.002 14 220 ∘ ∘ Example 8 1 82 130.002 14 220 ∘ ∘ Example 9 1 81 12 0.003 13 220 ∘ ∘ Example 10 0 83 180.003 19 660 ∘ ∘ Example 11 1 81 12 0.003 12 230 ∘ ∘ Example 12 1 81 120.002 12 230 ∘ ∘ Example 13 1 82 13 0.001 13 250 ∘ ∘ Example 14 1 83 300.001 30 >1000 ∘ ∘ Example 15 1 81 17 0.003 18 650 ∘ ∘ Example 16 1 8113 0.003 14 220 ∘ ∘ Example 17 1 82 11 0.005 11 120 ∘ ∘ Example 18 1 8211 0.003 12 220 ∘ ∘ Example 19 1 82 10.5 0.003 11 225 ∘ ∘ Example 20 182 10.0 0.003 10 225 ∘ ∘ Example 21 1 83 30 0.001 30 >1000 ∘ ∘Comparative 1 76 18 0.005 22 300 x x Example 1 Comparative 1 72 11 0.02220 30 ∘ x Example 2 Comparative 1 77 10.1 0.010 13 80 Δ x Example 3Comparative — 80 12 0.005 16 200 ∘ ∘ Example 4

INDUSTRIAL APPLICABILITY

As described above in detail, the filter cartridge of the presentinvention is well balanced in terms of properties such as aliquid-passing property, a filter life and a stability in a filteringaccuracy as compared with conventional bobbin-winder type filtercartridges and filter cartridges prepared by winding non-woven fabricsin a layer form. In particular, in case of a pleated matter prepared byconverging a strip, long fiber non-woven fabric in such a manner that atleast a part of the pleats is non-parallel, a filtering pressure in avertical direction to the pleats is less liable to apply as comparedwith a pleated matter having parallel pleats. Thus, the pleated matteris not crushed, and the filtering performance can more stably bemaintained.

1. A filter cartridge comprising a strip, spun bonded non-woven fabric,the fabric comprising a thermoplastic fiber in which at least a part offiber intersections is thermally adhered by a thermal compressionbonding method, wherein the strip, spun bonded non-woven fabric is woundaround a perforated cylinder in a twill form.
 2. The filter cartridge asdescribed in claim 1, wherein the thermoplastic fiber constituting thespun bonded non-woven fabric is a thermally adhesive composite fibercomprising a low melting point resin and a high melting point resin, thedifference in a melting point of both the resins being 10° C. or more.3. The filter cartridge as described in claim 2, wherein the low meltingpoint resin is linear low density polyethylene and the high meltingpoint resin is polypropylene.
 4. The filter cartridge as described inclaim 1, wherein the spun bonded non-woven fabric is bonded by thermalcompression by means of a heat embossing roll.
 5. The filter cartridgeas described in claim 1, wherein the strip, spun bonded non-woven fabricis twisted.
 6. The filter cartridge as described in claim 1, wherein thestrip, spun bonded non-woven fabric is formed into a pleated matterhaving 4 to 50 pleats and wound around said perforated cylinder in atwill form.
 7. The filter cartridge as described in claim 6, wherein atleast a part of the pleats of said pleated matter is non-parallel. 8.The filter cartridge as described in claim 6, wherein the pleated matterhas a void rate of 60 to 95%.
 9. The filter cartridge as described inclaim 1, wherein the filter cartridge has a void rate of 65 to 85%. 10.The filter cartridge as described in claim 1, wherein the strip of thespun bonded non-woven fabric has a width of 0.5 cm or more, and aproduct of the width (cm) and the basis weight (g/m²) is 200 or less.11. The filter cartridge as described in claim 1, wherein the filtercartridge has a ratio of trapped particle diameter in 0.2 MPa/initialtrapped particle diameter being 1–1.13 when initial trapped particlediameter is 7.1 to 30 μm.
 12. The filter cartridge as described in claim1, wherein the spun bonded non-woven fabric is bonded by thermalcompression by means of a heat flat calendar roll.